1. Field of the Invention
The present invention relates to a valve-operating mechanism in a 4-cycle engine and, more particularly, to an improvement in a valve-operating mechanism comprising a timing transmitting device having a driving rotary member connected to a crankshaft, and a cam device for transmitting a rotational force of a driven rotary member of the timing transmitting device as an opening/closing force to intake and exhaust valves mounted in a cylinder head.
2. Description of the Related Art
Such a valve-operating mechanism in a 4-cycle engine is already known, for example, as disclosed in Japanese Patent Application Laid-open No. 2000-161074.
As disclosed in the above Patent Publication, the cam device of the valve-operating mechanism is of a structure in which a cam having a relatively large diameter is obliged to be disposed immediately above the cylinder head, whereby the entire height of the engine is increased, which obstructs the compactness of the engine.
Accordingly, it is an object of the present invention to provide a valve-operating mechanism of the above-described type in a 4-cycle engine, wherein a cam of a cam device can be disposed on one side of c cylinder head, thereby reducing the entire height of the engine to contribute to the compactness of the engine.
To achieve the above object, according to a fist aspect and feature of the present invention, there is provided a valve-operating mechanism in a 4-cycle engine, comprising a timing transmitting device having a driving rotary member connected to a crankshaft, and a cam device for transmitting a rotational force of the driven rotary member of the timing transmitting device as an opening/closing force to intake and exhaust valves mounted in a cylinder head, wherein the timing transmitting device is disposed on one side of an engine body, and the cam device comprises a cam coupled to the driven rotary member of the timing transmitting device on one side of the cylinder head, intake and exhaust rocker shafts rotatably carried in the cylinder head, intake and exhaust cam followers secured to one ends of the rocker shafts with their tip ends in sliding contact with the cam, and intake and exhaust rocker arms secured to the other ends of the intake and exhaust rocker shafts with their tip ends abutting against the intake and exhaust valves.
The driving rotary shaft corresponds to a driving pulley 23 in an embodiment of the present invention, which will be described hereinafter, and the driven rotary member corresponds to a driven pulley 24.
With the first feature, the cam having a relatively large diameter is disposed on one side of the cylinder head, and the intake and exhaust rocker arms and the intake and exhaust rocker shafts having a relatively small diameter are disposed immediately above the cylinder head. Therefore, the valve-operating mechanism cannot be bulky above the cylinder head to contribute to a reduction in entire height of the engine an in its turn, to the compactness of the engine.
According to a second aspect and feature of the present invention, in addition to the first feature, a belt guide tube is integrally connected to the cylinder head with its upper end opened and accommodates the timing transmitting device; a head cover is coupled to the cylinder head and the belt guide tube to cover the timing transmitting device and the cam device from the above; and a support shaft supporting the driven rotary member and the cam and the rocker shafts are disposed above the coupled portions of the cylinder head, the belt guide tube and the head cover.
The coupled portions correspond to seal beads 87 in the embodiment of the present invention, which will be described hereinafter.
With the second feature, in a state in which the head cover has been removed, the support shaft and the intake and exhaust rocker shafts can be assembled and disassembled above the coupled portions of the belt guide tube and the cylinder head without being obstructed by the cylinder head and the coupled portions of the belt guide tube and the cylinder head, leading to improved assemblability and maintenance.
According to a third aspect and feature of the present invention, in addition to the first feature, the cam is rotatably carried at an intermediate portion of the support shaft rotatably supported at its opposite ends on the engine body.
With the third feature, the cam and the support shaft are capable of being rotated individually and freely. Therefore, during rotation of the cam caused by the timing transmitting device, the support shaft is also rotated in such a manner that it is dragged by the friction, whereby a difference between the rotational speeds of the cam and the support shaft can be reduced to reduce the wearing of rotational sliding portions. This can contribute to an enhancement in durability of the cam and the support shaft without use of a special material and surface treatment.
According to a fourth aspect and feature of the present invention, in addition to the third feature, the driven rotary member which is a driven pulley of the timing transmitting device is formed integrally on the cam and carried on the support shaft along with the cam, and the timing transmitting device is mounted to face the inside of an oil tank storing a lubricating oil and accommodating oil slingers for scattering the oil.
With the fourth feature, the oil scattered within the oil tank by the oil slingers can be sprinkled over a portion of the timing transmitting device and transferred to the entire timing transmitting device and the cam with the operation of the timing transmitting device to lubricate the timing transmitting device and the cam.